Protecting metal surfaces by corrosion inhibiting atmospheres



Unite 3,034,022 Patented Apr. 2, 1963 3,034,022 PROTECTING METAL SURFACES BY CGRROSION INHIEHTKNG ATMQSPHERES Guy G. Sindery, Burnham, England, assignor to Houseman 8.: Thompson Limited No Drawing. Filed June 20, N61, Ser. No. 118,2d4 9 Claims. (Ci. 21-25) The present invention relates to a method for treating metal surfaces and more particularly ferrous surfaces to protect them against corrosion.

Heretofore one known method of preserving ferrous surfaces for example the internal surfaces of boilers and pipes has been to maintain in proximity to those surfaces a vapour phase inhibitor such for example as cyclohexylamine carbonate or dicyclohexylamine nitrite, the inhibitor being allowed to vaporise to create an inhibiting atmosphere. The disadvantage of such materials is that they must be in close proximity to the surfaces and when preserving the internal surfaces of a boiler which is laid up for a period it is common practice to place inside the boiler trays of an inhibitor stacked at 4 to feet vertical intervals and arranged so that none of the internal surfaces of the boiler is more than 4 to 5 feet away from the inhibitor.

It has therefore not been possible heretofore to preserve the internal surfaces of long lengths of tube or other inaccessible surfaces by using this type of vapour phase inhibitor.

An object of the present invention is to provide a method for preserving metal surfaces and in particular ferrous surfaces against corrosion without the necessity of having the source of the inhibitor within close proximity to those surfaces.

Broadly the invention comprises passing over or through a supply of vapour phase inhibitor a gaseous medium at a temperature sufiicient to produce the required vaporisation of the inhibitor and then bringing the gaseous medium carrying the vaporised inhibitor into contact with the metal surfaces until there is established in contact with those surfaces an atmosphere carrying the inhibitor in vapour form and then sealing off the said surfaces and the said atmosphere from the outer atmosphere.

Preferably the gaseous medium employed in most cases is air and air at a suitable temperature for example 25 C. is passed over a tray of inhibitor for example cyclohexylamine carbonate or dicyclohexylamine nitrite. The use of heated air or other gaseous medium may be employed firstly to dry out the surfaces of the boiler or pipe or other piece of apparatus or equipment and secondly it is used so as to obtain an increased vaporisation of the inhibitor and generally it is desired to promote a supersaturated condition. In the case of the two inhibitors referred to above a temperature of 25 C. is suflicient but in some cases the temperature may be increased although in most cases a temperature over 100 C. is not desirable since some decomposition of the inhibitor may then take place.

When using cyclohexylamine carbonate or dicyclohexylamine nitrite the conditions including the temperature of the air or other gaseous medium employed should be such that generally 1500 cubic feet of air per pound of inhibitor should not be exceeded although as little as 1 pound of cyclohexylamine carbonate per 2500 cubic feet of air may be used usefully.

After the interior surfaces of the boiler pipes or other apparatus or equipment have been thoroughly dried out air or other gaseous medium is passed over the inhibitor to vaporise it and the air is then passed over all the surfaces to be protected until an inhibiting atmosphere is established.

After the interior surfaces of the boiler, pipes or other equipment have been completely dried and, by testing the air leaving the equipment at an outlet, establishing that a suitable inhibitor atmosphere is present in the equipment which contains a sufficient concentration of the inhibitor, the equipment is completely sealed off from the outer atmosphere by any suitable means. There is left inside the equipment a permanent inhibiting atmosphere which prevents corrosion by any residual moisture or by any moisture which may leak into the sealed off area.

If desired the atmosphere in the equipment may be controlled by the employment of an air conditioning plant through which the air is circulated in order to adjust to the required temperature and degree of humidity. A figure of 35 to 40% relative humidity is a good standard for establishing in the equipment a corrosion inhibiting atmosphere.

Instead of the air or other gaseous medium being circulated over trays containing the inhibitor there may be provided a self-supporting porous structure in which or upon the surfaces of which the inhibitor is carried, for example there may be provided a filter structure of glass wool, metal turnings, or Wood wool containing the inhibitor.

Whilst the invention can be employed for all surfaces where it is desired to establish a corrosion inhibiting atmosphere in contact with metal surfaces the invention has particular application to preserving the internal surfaces of containers such as of boilers and of pipes and enables the use of these inhibitors for preserving pipeways of considerable length, for example 1 /2 to 2 miles, when these pipes are laid up empty for any period.

This method of course is also applicable to any other piece of apparatus Where the metal surfaces to be preserved can be sealed off and if desired the complete apparatus both as regards internal and external surfaces can be laid up and preserved in this manner if the apparatus is encased in an envelope or other container which can be sealed, the interior of the envelope or other container being subjected to a through draught or heated gaseous medium carrying the inhibitor to dry off the apparatus and to establish in the container an inhibiting atmosphere. The invention has particular application where there are metal surfaces in particular ferrous surfaces which are remote or difficult of access, for example tubework in serpentine or tortuous form into which it would be impossible to establish by the heretofore known methods an inhibiting atmosphere.

Whilst normally air is the preferred gaseous medium it will be realised that other gases can be employed for example nitrogen or other insert gases where the presence of air is undesirable.

I claim:

1. A method of protecting a metal surface against corrosion which comprises the steps of:

(a) at least partially drying said metal surface,

(b) contacting a vapor phase inhibitor with a current of gaseous medium at a temperature sufficient to produce the required vaporisation of the inhibitor,

(0) passing said gaseous medium carrying the inhibitor vapor over said metal surface so that there is established over substantially the entire metal surface to be protected a concentrated atmosphere of the inhibitor, and

(d) sealing off said metal surface and inhibitor vapor form the outer atmosphere.

2. The process of claim 1 wherein the drying of said metal surface is effected by passing a drying atmosphere of said gaseous medium thereover.

3. The process of claim 1 wherein the vapor phase inhibitor is contacted with the current of gaseous medium and vaporised at a location remote from said metal sur- 1:3 face, and said gaseous medium carrying the inhibitor vapor is forced into contact with said metal surface.

4. The process of claim 1 wherein said gaseous medium is selected from the group consisting of air, nitrogen and other inert gases.

5. The process of claim 1 wherein the vapor phase inhibitor is selected from the group consisting of cyclohexylamine carbonate and dicyclohexylamine nitrate.

6. The process of claim 1 wherein the vapor phase inhibitor is carried by a porous structure and vaporisation thereof is effected by passing the gaseous medium through said porous structure.

7. The method of protecting the inner metallic surface of a container against corrosion which comprises the steps of:

(a) passing a drying atmosphere into said container and over said inner metallic surface,

(b) contacting a vapor phase inhibitor with a current of gaseous medium at a temperature sufficient to produce the required vaporisation of the inhibitor,

(c) passing said gaseous medium carrying the inhibitor vapor over said inner metallic surface so that there is established over substantially the entire inner metallic surface to be protected a concentrated atmosphere of the inhibitor, and

(d) closing said container so as to seal off said inner metallic surface and inhibitor vapor from the outer atmosphere.

8. The process of claim 7 wherein the atmosphere in contact with said inner metallic surface is adjusted to have a relative humidity of from to when the inhibitor vapor is passed thereover.

9. The process of claim 7 wherein the vapor phase inhibitor is contacted with the current of gaseous medium and vaporised at a location remote from said metal surface, and said gaseous medium carrying the inhibitor vapor is forced into contact with said metal surface.

References Cited in the file of this patent UNITED STATES PATENTS 2,634,223 Clendenin et al Apr. 7, 1953 2,996,35 Stobe Aug. 15, 1961 3,020,121 Bull Feb. 6, 962

OTHER REFERENCES Corrosion Prevention and Control, April 1957, pp. 37-39.

Baker: Volatile Rust Inhibitors, NRL Report 4319, March 10, 1954, p. 12. 

